The present invention is in the field of plastic film and especially in the field of large sheets of thermoplastic film generally referred to as greenhouse film.
Greenhouse film is a type of thermoplastic film made for covering greenhouses or other similar type hot houses used in growing plants and the like. Such film is customarily manufactured in large sheets. The sheets generally range in widths from about 10 feet to about 50 feet with lengths running from about 50 feet to about 500 feet. The film is also produced in various gauges, but usually has a thickness of about four mils to about six mils. Larger or smaller sizes can be made, but such are generally not desirable for most commercial uses.
Greenhouse film is presently manufactured as an elongated relatively flat tube of a predetermined length, width and gauge. For some purposes, the film is slit longitudinally on one side so that the film may be opened into a single flat sheet of about double the width of the flat tube.
These large sheets of thermoplastic film must be folded and packaged for storing and shipping to an end user. In order to facilitate their installation on a greenhouse, they are folded in a particular manner.
One type of fold employed in packaging greenhouse film that has been well received in the marketplace is a "U" type fold which is packaged as a roll which permits an installer of the film to center the roll on the apex of a roof or roof frame of a greenhouse, unroll the film the length of the greenhouse and then unfold the film to its full width down each side of the greenhouse. Such type of film fold construction is described in U.S. application Ser. No. 423,955, filed on Sept. 27, 1982, and which is hereby incorporated herein.
The handling of large sheets of thermoplastic film and the folding thereof are difficult and present a number of problems. It is important that the film be folded symmetrically, without hard folds, and be wrinkle-free. Often, it is necessary that films of various widths be manufactured more or less continuously.
It is, therefore, a principal object of the present invention to provide an apparatus which makes a "U" shaped fold of large sheets of plastic film, such as greenhouse film.
It is an important object of the instant invention to provide a plastic film or sheet folding apparatus which folds wide sheets of the film without the film having hard folds or obtaining wrinkles.
Another object of the invention is to provide an apparatus which provides for the continual folding of wide sheets of thermoplastic film of various widths into a "U" shaped fold.
Still another object of the present invention is to provide an apparatus which continually folds wide sheets of thermoplastic film into a "U" shaped fold quickly, easily and symmetrically.
These and other objects of the invention will become more readily apparent from a reading of the specification and drawings hereinafter.